Allowance for credit losses - Troubled debt restructurings loan count by type of modification (Details) - loans	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable
Loan count	619	547	1,911	1,685
Reduction in interest rate
Financing Receivable
Loan count	61	161	302	896
Extension of maturity date
Financing Receivable
Loan count	71	49	257	127
Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	458	70	1,286	237
Other
Financing Receivable
Loan count	29	267	66	425
Construction
Financing Receivable
Loan count		1		1
Construction | Reduction in interest rate
Financing Receivable
Loan count		0		0
Construction | Extension of maturity date
Financing Receivable
Loan count		1		1
Construction | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count		0		0
Construction | Other
Financing Receivable
Loan count		0		0
Mortgages
Financing Receivable
Loan count	507	348	1,426	609
Mortgages | Reduction in interest rate
Financing Receivable
Loan count	13	0	35	2
Mortgages | Extension of maturity date
Financing Receivable
Loan count	35	24	114	50
Mortgages | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	455	70	1,273	231
Mortgages | Other
Financing Receivable
Loan count	4	254	4	326
Commercial | Commercial multi-family
Financing Receivable
Loan count		1	2	2
Commercial | Commercial multi-family | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Commercial | Commercial multi-family | Extension of maturity date
Financing Receivable
Loan count	0	1	1	2
Commercial | Commercial multi-family | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	0
Commercial | Commercial multi-family | Other
Financing Receivable
Loan count	0	0	0	0
Commercial | CRE non-owner occupied
Financing Receivable
Loan count	1	2	10	5
Commercial | CRE non-owner occupied | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Commercial | CRE non-owner occupied | Extension of maturity date
Financing Receivable
Loan count	0	2	9	4
Commercial | CRE non-owner occupied | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	1	0	1	0
Commercial | CRE non-owner occupied | Other
Financing Receivable
Loan count	0	0	0	1
Commercial | CRE owner occupied
Financing Receivable
Loan count	4	7	35	26
Commercial | CRE owner occupied | Reduction in interest rate
Financing Receivable
Loan count	0	0	3	0
Commercial | CRE owner occupied | Extension of maturity date
Financing Receivable
Loan count	0	7	23	26
Commercial | CRE owner occupied | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	3	0
Commercial | CRE owner occupied | Other
Financing Receivable
Loan count	4	0	6	0
Commercial | Commercial and Industrial
Financing Receivable
Loan count	11	12	26	39
Commercial | Commercial and Industrial | Reduction in interest rate
Financing Receivable
Loan count	1	0	2	1
Commercial | Commercial and Industrial | Extension of maturity date
Financing Receivable
Loan count	2	12	10	38
Commercial | Commercial and Industrial | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Commercial | Commercial and Industrial | Other
Financing Receivable
Loan count	8	0	14	0
Consumer | Credit card
Financing Receivable
Loan count	31	82	148	699
Consumer | Credit card | Reduction in interest rate
Financing Receivable
Loan count	19	69	108	621
Consumer | Credit card | Extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Consumer | Credit card | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	0
Consumer | Credit card | Other
Financing Receivable
Loan count	12	13	39	78
Consumer | Home equity lines of credit
Financing Receivable
Loan count			2	2
Consumer | Home equity lines of credit | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Consumer | Home equity lines of credit | Extension of maturity date
Financing Receivable
Loan count	0	0	1	1
Consumer | Home equity lines of credit | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	1
Consumer | Home equity lines of credit | Other
Financing Receivable
Loan count	0	0	0	0
Consumer | Personal loans
Financing Receivable
Loan count	59	92	245	273
Consumer | Personal loans | Reduction in interest rate
Financing Receivable
Loan count	28	91	148	269
Consumer | Personal loans | Extension of maturity date
Financing Receivable
Loan count	31	1	94	3
Consumer | Personal loans | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	0
Consumer | Personal loans | Other
Financing Receivable
Loan count	0	0	2	1
Consumer | Auto Loan
Financing Receivable
Loan count	4	1	8	12
Consumer | Auto Loan | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Consumer | Auto Loan | Extension of maturity date
Financing Receivable
Loan count	3	1	5	2
Consumer | Auto Loan | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	1	0	3	2
Consumer | Auto Loan | Other
Financing Receivable
Loan count	0	0	0	8
Consumer | Other
Financing Receivable
Loan count	1	1	7	3
Consumer | Other | Reduction in interest rate
Financing Receivable
Loan count	0	1	6	3
Consumer | Other | Extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Consumer | Other | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Consumer | Other | Other
Financing Receivable
Loan count	1	0	1	0
Leasing
Financing Receivable
Loan count	1		2	14
Leasing | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Leasing | Extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Leasing | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	1	0	2	3
Leasing | Other
Financing Receivable
Loan count	0	0	0	11